Re: GNU Radio web API

[Marcus Müller]

Hi Kevin,

you're kind of right:

On 25/06/2020 05.34, Kevin Reid wrote:
> There is unfortunately 
> no standard way to tell a block to free the resources it is using, other 
> than ensuring it is "deleted" by dropping all references to it. 

Well, technically, when a flow graph is finished running, the stop() 
methods are called for that very reason. But then you can't reconnect.

We never thought about the proper semantics for that function. IMHO, we 
would have needed a "prepare for reconfiguration" state. And, we would 
have needed an explicitly defined state machine to begin with to not end 
up in a million different states...

> Therefore, you need to ensure that your Python code does not have any 
> variables or attributes referring to the old top block or the individual 
> blocks, before you construct the new blocks.

Even then, Python garbage collection is non-deterministic, I think .

> That said, you may want to try the alternative of keeping the UHD, 
> socket, etc. blocks around and reusing them, and only changing what 
> they're connected to. (That's what ShinySDR currently does, though with 
> different blocks.) Basically, use disconnect() as well as connect() to 
> change your flow graph's connectivity while it's stopped so that it 
> suits the new purpose. You might encounter some misbehavior here too, 
> though; this is not a frequently used and well-tested part of GNU 
> Radio's capabilities.

Absolutely true, sadly.
Fun fact, there's now multiple research institutions spending 
braingrease on this, hopefully we'll find a solution to this whole 
problem soon.

Best regards,
Marcus

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